Predicting the response of wheat (Triticum aestivum L.) to liquid and granular phosphorus fertilisers in Australian soils

Liquid forms of phosphorus (P) have been shown to be more effective than granular P for promoting cereal growth in alkaline soils with high levels of free calcium carbonate on Eyre Peninsula, South Australia. However, the advantage of liquid over granular P forms of fertiliser has not been fully investigated across the wide range of soils used for grain production in Australia.We report results of a large glasshouse pot experiment undertaken with 28 diverse soils ranging from acidic through to alkaline non-calcareous collected from all over Australia to test if liquid P was more effective for growing spring wheat (Triticum aestivum L.) than granular P. Liquid P produced greater shoot dry matter responses, as measured after 4 weeks growth (mid to late tillering, Feeks growth stage 2-3) than granular P in 3 of the acidic to neutral soils and in 3 alkaline soils. Shoot dry matter responses of spring wheat to applied liquid or granular P were related to soil properties to determine if any of the properties predicted superior yield responses to liquid P. Only the calcium carbonate content of soil predicted when liquid P was more effective than granular P.Five soil P test procedures (Bray, Colwell, resin, isotopically exchangeable P and diffusive gradients in thin films (DGT)) were used to measure soil test P on subsamples of soil collected before the experiment started. These soil test values were then related to the dry matter shoot yields to assess their ability to predict wheat yield responses to P applied as liquid or granular P. All five soil test procedures had similar ability to predict yield responses to applied P as either liquid or granular P, with the resin P test having a slightly greater predictive capacity on the range of soils tested.